In the production of electrical and electronic components in which materials are joined, it is imperative to achieve a good quality joint in order to increase the reliability of such components. High energy welding techniques, such as laser or electron beam welding, are capable of generating extremely localized high energy beams resulting in unique advantages when welding small workpieces or components. The integrity of such welding techniques is determined by analyzing the resulting welds. Such analysis may vary from a mere visual inspection of the welded joint on the workpiece to a detailed post-welding X-ray, ultrasonic, or infrared examination of the welded workpiece or component. Often, destructive methods are used to evaluate the joining technique by testing samples, rather than all, of the components produced.
In order to achieve a more reliable evaluation technique, several known nondestructive testing methods were developed to analyze the integrity of high energy welding techniques. One of such known methods described in U.S. Pat. No. 4,007,631 uses Stress Wave Emission (SWE) techniques also referred to as Acoustic Emission (AE) techniques, to monitor the quality of a laser weld. In accordance with this known method, which has proven to be effective and accurate, a piezoelectric transducer is attached to one of the parts to be welded or is mounted on a fixture which is in contact with at least one of the parts. The transducer converts the acoustic emission (AE) signals generated within the parts being welded during the welding operation into an electrical signal for further processing. When welds are to be made on a large number of parts located on a single fixture, multiple transducers are required since reflections and attenuations of the AE signals prevent the use of a single transducer. Furthermore, if the high energy welding technique is performed on relatively small pieceparts or components, it becomes difficult to physically attach the transducer to such a small part for AE signal detection.
Therefore, there exists a need for a noncontact, nondestructive method for monitoring the quality of welds during the welding process.